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Comment by dredmorbius | Hacker News Reader

NB: The infographic and articles are based on a 1993 publication.

More recent research, from about 2017, suggests that there's about as much water in Earth's mantle as in all the oceans, so we either need another drop roughly the volume of the first, or the second drop should be greatly expanded.

See: "There’s as much water in Earth’s mantle as in all the oceans" (2017) <https://www.newscientist.com/article/2133963-theres-as-much-...>

The USGS is citing a 1993 publication, Igor Shiklomanov's chapter "World fresh water resources" in Peter H. Gleick (editor), Water in Crisis: A Guide to the World's Fresh Water Resources (Oxford University Press, New York) (see the detail links from the submitted article).

That said, water remains a precious resource, and fresh surface water all the more so.

Edit: /double the size/s/size/volume/ above, for clarity.

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> More recent research, from about 2017, suggests that there's about as much water in Earth's mantle as in all the oceans, so we either need another drop roughly the size of the first, or the second drop should be greatly expanded.

Specifically: given that the volume of a sphere is 4/3πR^3, doubling the volume is equivalent to increasing the radius by ~26%.

Good call, I've swapped "size" for "volume" to be clearer.

> The water discovered in the mantle is not in a form familiar to us – it is not liquid, ice, or vapor. Instead, it is trapped inside the molecular structure of the minerals in the mantle rock.

IMHO this is not a productive comparison. Hydrogen and oxygen ions inside minerals in rock is far too much of a stretch of imagination to call as water.

https://www.earth.com/news/ringwoodite-mineral-confirms-vast...

> Hydrogen and oxygen ions inside minerals in rock is far too much of a stretch of imagination to call as water.

Agreed and to follow that thread to the end: We can't impact that water in a meaningful way.

We can't pollute it in dozens of ecosystem-altering ways.

We can't alter it's ability to host systems that sustain life.

We can't bulk-melt the frozen part & in turn alter the salinity + elevation of a liquid part.

We can't pump dry the parts that we desperately need to remain where they are.

Are you sure we can’t do any of these things, or are you just not thinking big enough? Give me a couple million dollars of VC money and I bet I could have an MVP that could conceivably accomplish at least one of these. I’d obviously need to raise another round of funds to find a market for such a product before taking the necessary steps to fit my product into that particular market (after raising more funds again, obviously). This hypothetical startup could be a net benefit to investors and shareholders by 2035, and a net detriment to all others by 2028. “Disruptive” is an understatement for what we could do for the environment and society.

If you had the means to reach the mantle economically, there are a lot of other uses you'd be put to first. Magma geothermal comes to mind.

I don't think it's "hydrogen and oxygen ions"; that doesn't really meet the definition of water. I'd assume it's more like ebsom salts, where H2O is a part of the crystalline structure of the chemical compound. If you heat up epsom salts enough then the bonds are broken and steam is released.

When I see these infographics I think of non-technical audiences like policy makers and politicians consuming the same information, and I avoid making these fine distinctions. In this case, I would not mention the water in the mantle at all.

In a separate, private graphic, I’d show the available water next to the number of 1 GW reactors, the pile of annual uranium mining output to feed those reactors, and annual calendars it would take to assemble all that to extract the water and dispose of the waste in a way that won’t harm our ecosystem further to express, “if you want this water in a form you colloquially understand, the species possibly can’t afford it”. In case some wise ass decides to bring up that mantle water. But that additional detail would even help technically inclined audiences reading the infographic.

Does any of that water, though, ever make it onto the Earth's surface? I'm guessing not, or only miniscule amounts over geologic time through volcanism.

For all intents and purposes, I think only counting "surface" water is more useful and intuitive. It's essentially any water that can participate in the hydrologic cycle on Earth, and that water locked beneath the crust doesn't really "matter" for what I think the intended purpose of this graphic is.

The fundamental problem with complex phenomena is in defining the domain(s) of interest.

If we want to talk about the total amount of H2O around, on, or in the Earth then inclusion makes sense.

If we want to talk about water interacting with the surface environment (atmospheric, sea, ice cap, fresh, and subsurface aquifers and tectonic water), then splitting those into distinct categories probably also makes sense. In which case we can also show the subsurface water.

How much mantle water does make it to the surface over time is a good question. I've no idea though I'd suspect that some does through geothermal and tectonic activity. The more interesting question might be how we'd determine this (all but certainly through isotopic composition), and if a net flux could be determined.

Over geological time, additional reservoirs of water are significant simply because surface water boils off into space over time, with estimates I've seen of up to 25% of Earth's original allotment having done so over 4.5 billion years or so. As the Sun eventually grows warmer, this rate will increase. At the same time, tectonic activity will slow.

Note that there's a fair bit of water transport through the lower crust / upper mantle as oceanic plates subduct under continental plates, with the water absorbed into the oceanic plates playing a major role in volcanism at those plate boundaries, e.g., along the "Rim of Fire" surrounding the Pacific basin.

Earth is lucky to have a strong magnetic field and ozone layer limiting the loss of hydrogen to the solar wind. Mars, for example, has lost much more of its allotment.

We don't have access to any part of the planet below a depth of 2.5 miles, so the image should compare the volume of accessible water to the volume of accessible Earth, except then it would fail in its dishonest mission to make people say "gosh that sphere looks relatively small compared to the other sphere, I must restrict myself to ten-second showers."

Even if it was accessible water to accessible non-water I don't really see how the metric is relevant in any decision making. Is it warning against a half-baked plan to mix water with every available cubic meter of soil or rock? Because there wouldn't be enough water to do that crazy thing? Thanks, I'll bear that in mind.

>We don't have access to any part of the planet below a depth of 2.5 miles

Given how many miles I can travel over land or through the air, 2.5 miles _into_ the earth is amazingly shallow in similar ways to how the article already anticipated my amazement of how small the spheres of water were.

You seem really upset about what to me looks like a quite neutrally presented fact. There are lots of interesting aspects to this picture which don't have anything to do with criticizing you or the length of your morning shower.

It’s just an interesting infographic that is factually correct. You can disagree that the chosen facts are relatively the best ones, but, not everything has to have an agenda. Calling facts dishonest because they make you uncomfortable is what I consider yucky.

I think a neat follow-up image would be a sphere containing the top 2.5 miles of Earth’s crust for comparison to the water.

The article has a strong focus on "available to humans" and "that humans depend on". Many of the water beneath the crust is exactly that, pumping it up is an important source of drinking water. (In my country, the Netherlands, it's the primary, almost only, source of drinking water)

The Netherlands doesn't pump water from beneath the crust! Groundwater is included in the larger freshwater sphere. Water in the mantle would be an additional sphere (not sure if it's freshwater or saltwater).

TIL. I did not get that that from the article. Thanks for correcting me.

I simply presumed that water that's pumped from layers 100m or lower below the surface, water that's sometimes 10.000 years "old", wasn't surface water. But it makes sense to lump it in there too.

The crust is about 40km thick. The deepest anyone has ever dug is ~12km[0]. It is quite weird to think we live on this crust which has a gigantic mass inside that we can't get to.

[0] https://en.wikipedia.org/wiki/Kola_Superdeep_Borehole

If you think that's weird, you'll love this. Go look at another human. There's a skeleton in there!

PFAS have reportedly contaminated water everywhere on Earth including the water in springs, confined aquifers, and even the rain that falls.

Is the water pumped from beneath the crust in the Netherlands poisoned too or have you guys got the last of the good stuff?

An interesting point, perhaps it's just me, but my initial reaction to this was that, for purposes of comparison, the volume of "usable" or maybe inhabitable land be measured instead, as opposed to the volume of the entire planet including mantle, core, etc. this graphic seems very prone to misinterpretation and usage as a memetic weapon against globalization, as it is.

It's similarly misleading to color coding a map of a nation's or a region's land area to show how the people who occupy various parts of that land area voted in an election. The graphic representation tells a story about the land that deceptively implies facts about the people that are not true.

I completely agree with you. Let's add to the fact that volume, being three-dimensional, is being represented on two dimensions (graphics on a computer screen), which might cause some loss of perspective, fundamental for comparison. Perhaps a better way to represent it would have been the volume of inhabitable land (as you suggest) vs the volume of available water but extrapolated to two dimensions?

It does separate liquid fresh water from surface lakes and rivers which makes me believe the middle ball includes reasonably accessible ground water.

My read is that the two smaller spheres are non-exclusive, and that the smallest is included in the 2nd.

The breakout is for comparison: surface freshwater (total) and surface freshwater (lakes and rivers) relatively.

Yes they're pretty clearly subsets of each other. There's a better graphic on this page: https://www.usgs.gov/special-topics/water-science-school/sci... Direct link: https://d9-wret.s3.us-west-2.amazonaws.com/assets/palladium/...

That one actually has percentages on the subsets too for interesting differences like glacier and icecap volume vs ground water (which I think still excludes the kind of deep mantle water mentioned up thread because it's not usably extractable).

> or the second drop should be greatly expanded.

The second drop is called "liquid fresh water".

I'm not sure if I would want to categorize the water in the mantle as either "liquid" or "fresh". Most of that stuff is way above the critical point, not to mention saturated with rocky salts.

> second drop should be greatly expanded

Radius of said sphere would only increase by ∛2. ;)

Seems that Jules Verne (1867) in 'Journey to the Center of the Earth' was onto something when he invented his subterranean ocean.

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